The bright side of a currency decline is supposed to be rising exports. But in key emerging markets around the world, that isn’t happening.

Currencies in some countries are hitting new lows, down as much as 30% in the past 2½ years. Meanwhile, emerging-market export growth has fallen to its lowest levels in more than half a decade. Exports themselves fell 14.3% year over year in the three months through May, the biggest decline since 2009, according to Capital Economics.